This invention relates to a nuclear magnetic resonance spectrometer, and more particularly to an impulse resonance spectrometer wherein high frequency energy in the shape of pulses is applied to a sample material located in a polarizing magnetic field, to detect the nuclear magnetic resonance signal of the sample material.
It is known that when high frequency energy at an angular frequency .omega. is applied to a sample material located in a polarizing magnetic field denoted by H.sub.o, a nuclear magnetic resonance is caused by fulfilling the relationship .omega.=.gamma.H.sub.o where .gamma. denotes the gyromagnetic ratio of a measured nucleus.
According to the condition of the nuclear magnetic resonance, only a signal having one peak ought to appear. However, a signal having many peaks appears under the influences of the electro-negativity of an adjacent atom or group based on a molecular structure, any magnetic anisotropy, and/or the polarizing magnetic field. This split is called the chemical shift.
The chemical shift is useful in that the molecular structure of the sample material can be discriminated by reading the difference between the peak of the resonant line of tetramethylsilane (TMS) usually employed as a reference material for measuring the chemical shift and the peak of another spectrum, that is, the difference between frequencies.
The nuclear magnetic resonance spectra, however, include besides the chemical shift another split attributed to the fact that two or more spins of the nuclei exhibiting the magnetic resonance have interactions among them. This split is called the spin-spin coupling.
The spin-spin coupling principally occurs between molecules whose coupling states with the hydrogen nucleus are approximate.
The utility of researches on molecular structures doubles owing to the split of the nuclear magnetic resonance signal attributed to the interaction in the spin-spin coupling. On the other hand, however, the nuclear magnetic resonance signal becomes complicated, and the interpretation and analysis thereof are not simple.
Further, it is known that when the second high frequency energy H.sub.2 is applied to one nucleus in the spin-spin coupling generated by applying the first high frequency energy H.sub.1 to the sample material, the other observed nucleus apparently has the spin-spin coupling erased or changes in the magnitude of coupling or splits, so spectra different from the original resonance signal are observed. Thus, the situation of the interaction between the nuclei can be known, and simultaneously the split based on the spin-spin coupling and the split based on the chemical shift can be discriminatively observed.
The method of measurement which is performed by applying the two different sorts of high frequency energies H.sub.1 and H.sub.2 to the sample material is called the spin decoupling. The spin decoupling is a measurement method which is indispensable especially to the analysis of the resonance spectra of the hydrogen nucleus.
An impulse resonance spectrometer which detects a nuclear magnetic resonance signal by applying the first high frequency energy in the shape of pulses to a sample material located in a polarizing magnetic field has been known from, for example, U.S. Pat. No. 3,475,680.
To carry out the spin decoupling in a continuous wave resonance spectrometer wherein a nuclear magnetic resonance signal is detected by applying the first high frequency energy H.sub.1 in the shape of continuous waves to a sample material located in a polarizing magnetic field, has been known from, for example, U.S. Pat. No. 3,348,137.
However, there has not been known yet the concrete construction of an impulse resonance spectrometer in which in performing the spin decoupling by applying the second high frequency energy H.sub.2 to a sample material, the frequency of the second high frequency energy H.sub.2 can be precisely measured from a nuclear magnetic resonance signal and the first and second high frequency energies can be held stable for a long time.